1. Field of the Invention
The present invention relates to a method of processing a colored image in multilevel gradations, and more particularly to a method of processing a colored image in multilevel gradations to produce a halftone or intermediate-tone image through a multilevel area gradation process employing multiple thresholds.
2. Description of the Prior Art
Various digital colored image forming processes used in color copying machines, color printers, color printing technology, and the like carry out a multilevel area gradation process employing multiple thresholds for producing a halftone or intermediate-tone image by using a plurality of colors. According to such a method of processing a colored image in multilevel gradations, the more multilevels are used, the better the gradation and hence the greater the quality of a colored image.
If the number of multilevels used is increased in order to improve the gradation, the processor required to process the image would be rendered complex, resulting in an increased number of processing circuits and a higher cost. For example, signals indicative of four colors such as yellow, magenta, cyan, and black may be processed in three bits with 8 levels, and signals representing these four colors may be processed in two bits with 4 levels. The ratio of the cost of former process to the cost of the latter process is 3 : 2. If the number of multilevels used is reduced, the cost of the process would be lowered, but the quality of a resulting colored image would also be lowered. Therefore, the number of gradations should not be excessively lowered in order to maintain a certain desired image quality.